Papermaking machine having a polyethylene suction box top



Feb. 8, 1966 R. POESCHL ETAL PAPERMAKING MACHINE HAVING A POLYETHYLENE SUCTION BOX TOP 2 Sheets-Sheet 1 Filed Feb. 4, 1963 Feb. 8, 1966 R. POESCHL ETAL PAPERMAKING MACHINE HAVING A POLYETHYLENE SUCTION BOX TOP 2 Sheets-Sheet 2 Filed Feb. 4, 1963 {Ci 66TH? United States Patent Ofiice 3,234,079 Patented Feb. 8, 1966 k 3,234,079 PAPERMAKING MACMNE HAVING A POLY- ETHYLENE SUCTKON 30X TOP Rudolf Poeschl, 135 Mariahiiferstrasse, Vienna, Austria, and Wilhelm Pocschl, Rohrhach, Oberosterreich. Austria Filed Feb. 4, 1963, Ser. No. 256,059 Claims priority, application Austria, Feb. 7, 1962, A 996/62; May 11, 1962, A 3,890/62 24 Claims. (Cl. 162-374) Machines for extracting water from paper and pulp are in continuous Operation in most cases during the day and night and their output depends on the speed of the machine wire. For this reason an increase in the speed of the Wire will result in a proportional increase in output. On the other hand, a certain extraction of water from the stock must be effected in the Wire end of the machine under the action of the vacuum on the wire. if the speed of the wire is increased, the vacuum action on the wire must also be increased. This involves an increase in the pressure with which the Wire is forced on the suction box tops so that the friction between the wire and the suction box tops is increased in the same proportion and with it the tension required for driving the Wire. The wire is driven by the couch roll. At a given tension of the wire, only a limited driving force can be transmitted by the couch roll to the Wire. On the other hand, the number of the wire in a paper machine depends on the grade of paper to be manufactured so that the number of the wire cannot be increased. In the known paper machines, the speed of the wire is so chosen as to reach just the limit at which the drive of the Wire by the couch roll is ensured under a vacuum action sufiicient for the required extraction of water at this speed of the wire whereas the allowable stress of the wire is not exceeded. Hence, an increase in the speed of the wire and an increase in output cannot be achieved with the known machines.

Becausein these known machines the wire is loaded to the allowable limit, a relatively rapid wear of the wire must be expected. This requires a relatively frequent replacement of the wire. Considerable costs and a shutdown of the machine are involved in the renewal of the wire. Because such machines are in continuous operation during the day and night, as has been mentioned before, this shutdown results in a reduction in output. To reduce the wear of the wire, it has already been proposed to make the suction box or forming board tops of a plastic which is softer than the material of the wire so that the wear of the latter is reduced. While this enables an increase in the intervals of time after which the wire must be replaced, the wire is still subject to considerable wear and the output of the machine cannot be increased. Suchsuction box tops consist of plastic plates on a backing consisting, e.g., of Wood or metal. This twolayer material has the disadvantage that the walls of the holes in the suction box tops are uneven, particularly at the joint between the two layers, and these uneven portions promote an accumulation of sucked-off fiber material on the Walls of the holes so that the holes in the suction box tops 'are gradually reduced in cross section. For this reason, such suction box tops must be frequently cleaned, which results again in'a shutdown and reduction in output.

It is an object of the invention to eliminate these disadvantages and to increase the output of machines for extracting water from paper or pulp. The invention resides in a machine for treating paper or pulp, a machine wire for receiving the material to be treated, means, such as at least one suction box and/or at least one forming board for extracting water from the material to be treated, said means having sliding surfaces on'their tops, on which the machine wire slides, said tops consisting of a polyethylone plastic softer than the material of the wire, whereby the coeificient of friction between the machine Wire and the tops is less than 0.12, so that the speed of the wire is increased by a reduction of the slip of the wet wire driving roller and whereby the tops made only from this plastic are stable in shape and self-supporting and have an active water-extracting area of at least 40% of the waterextracting zone to increase the extraction of water from the stock. In conjunction with the fact that the material of the suction box and/or forming board tops is softer than the material of the machine wire, the low coefficient of friction of the plastics used ensures a particularly low wear of the wire and it has been found that the wear of the suction box and forming board tops is extremely small. As a result, stoppages for a replacement of the wire will be minimized. Owing to the reduction of the frictional resistances, the active water extracting area of the suction box tops can be increased, which results in an increase of the rate at which water is extracted from the stock so the speed of the wire can be increased whereas the tensile stress required in the wire to enable a substantially slipfree drive thereof by the couch roll does not exceed the allowable stress. In this connection, the term active water extracting area is the ratio of the area of the openings in the suction box tops to the entire area of a rectangle which defines the water extracting zone, as will be explained with reference to the drawing.

It has been found that the narrow lands remaining between the suction holes if the forming board and/or suction box tops are designed according to the invention and a relatively large active suction area is provided, will not break out because the material withstands the stresses involved in surfacing the tops. The fact that the suction box and/or forming board tops are stable in shape and self-supporting has the further advantage that the need for the previously required backings for the suction box and/ or forming board tops is eliminated. As a result, the joint formed between the two layers at the walls of the holes and promoting an accumulation of fiber material is also eliminated and the cleaning of the suction box and forming board tops, which cleaning involves a shutdown, may be performed in much longer intervals of time. The known backings consisting, e.g'., of wood, have always involved difficulties because their degree of swelling was different from that of'the material of the suction boxes so that warping occurred, which had to be eliminated by subjecting the table top to a time-consuming surfacing operation.

The materials used according to the invention for the suction box and/ or forming board tops are stable up to temperatures above C. This affords the advantage that the stock can be applied in boiling condition without damage to the forming board and/or suction box tops. The application of the stock in boiling condition has become increasingly popular in recent years. In a preferred embodiment of the invention, sintered low-pressure polyethylene having a molecular weight of about 1,000,000 is used as a plastic. This material has a particularly high impact strength so that forming board and/ or suction box tops made from this material can be surfaced by surfacing machines having surfacing knives rotating at high speed. It has been found suitabe to charge this material as a powder into an elongated mold and to sinter it there under a high pressure and at "an appropriate temperature. Plates of any desired size which are made from such material have a particularly low coefficient of friction with respect to the wire so that the coefiicient of friction between the wire, on the one hand, and the forming board and/or suction box tops, on the other hand, may be reduced below 0.1, in accordance with the invention. In spite of the resulting further increase in the speed of the wire, a satisfactory extraction electrically conducting. These admixtures may be added. in the form of powders and may consist of molybdenum sulfide powder or molybdenum disulfide powder, on the one hand, and graphite powder, on the other hand. The

total amount of these admixtures isless than percent by weight, preferably between 1 and 3 percent byweight. At high speeds of the wire, adverse circumstances may coact to cause an electrostatic charging of the suction:

boxand/ or forming board tops. This electrostatic charge may result in an accumulation of dirt, which may build. up to the size of afingernailand is then suddenly torn off into the path of the stock. Such a charging of the tops maybe prevented by theelectrically conducting ad-.

mixtures added to. the plastic material of the suction box and/ or forming board tops The electrically conducting admixtures impart to, the suction .box and/or forming board top such a conductivity that the electrostatic the resistance to acid, the stability of shape, the resistance to swelling, low wear and temperature stability etc; In stead of molybdenum sulfide or molybdenum disulfidegon the .one. hand, and graphite'powder, on the other hand, other substances which reduce friction and/or impart electrical conductivity may be added to the PIZIS-r' tic. For instance, the plastic material may contain about i /2 percent by weight of molybdenum sulfide powder or molybdenum disulfide powder and about /2 percent by weight-of graphite powder. These additions of dry hlbIl-i cants result in a particularly; great reduction of the friction;

betweenthe suction box tops and the wireand thus enable a considerable increase in the suction effect and wire speed resulting in a considerable increase in output. It hasbeen found that in this way the wire speed and the output can. readily be increased by about while a satisfactory extraction of water from the stockiis maintained.

The particle sizes of theadmixture will depend on the nature of the plastic material to .be processed and on;

the nature of :the friction-reducing or electrically conducting admixtures. According tothe invention, the particle size of the admixtures may be between 5 microns and 0.05 micron, preferably in the range between 2 microns and 0.2 micron; Favorable: results are obtained,

e.g., with molybdenum sulfide powder having a particle size below 2 microns, and best results are achieved with particle sizes of 0.4 micron orv 0.2 micron.

In the manufacture of the suction box and/orforming board tops of plastic, the admixtures in powderformare added to the plastic powder. Thisis followed bymixing and subsequently the tops can be made by sintering, molding, extruding or the like. The plastic material will establish'an intimate bond with the admixtures.

It is also possible within the .scope of the invention tomake the suction box and/or forming board tops in one piece in order to avoid vacuum defects which would interrupt the operation. This is of special importance because, even very small disturbances in the charging and distribution of .thestockon the wire will result in undesirable effects in the finishedroll. If the paper does not summation of micro defects; For this reason it-is highly desirable that the suction box and/ or forming board tops l 4 have a uniform thickness throughout, the roll cannot be cylindrically wound but will have thumps due to a repeated should be maintained as truly planar as possible in order to avoid. animpression of'uneven portions into .the stock.

The planar form of the; suction box and/ or forming board.

tops can best be maintained if they are-made in one piece;

Alternatively, suitably shaped elements which. are =conveniently interconnected may be used. 7

Withinthe scope of :the invention, best results will be obtained if-that surface of the suction box and/ or form-;

ing board top which. cooperates with the .wireis polished, preferably to :a high finish.-. In this case, extremely low coeflicients of friction may easily begobtained; these values may be less than 0.095 or even less than 0.09.,

In connection ,with the. known'forming board and/ or suction box tops, the stock inevitably entrained by the water, draining through the wire wasv able to buildup in the holes of, thelformingboard ,top because these holes were always fairly rough, particularly underthe influence ofthe moisture; For this, reason it has: been attempted to provide suction box tops with upwardly tapering. holes toprevent an interruption of the .vacuum by entrained stock built up in the holes. templates the provision gof. ;suction holes which zare polished, preferably toa high finish so that a build-up ofthe entrainedstockon the walls of. the suctionholes is prevented to alargeextent. V portance that therperfect smoothness of the highly finished holes is maintained during the operation because the ma-v terials usedtiaccording to the invention are resistantito acids and alkalies inaconcentrationsup to 5% at tempera-; tures much above C. Otherwise the high finish of the suction holes would soon'be destroyed bythe. action of acids and/Oraalkrlies. to a high finish is facilitated by the ease with which the materials used according to the inventionycan be ma+.-

chined. I Machining can easily be. carried outin a simple manner with all wood-working t00ls, includ-ing milling This. is prompted by another property of sinteredv cutters. lowspressure polyethylene having a high molecular weight,

and of molded or extruded polyethylene or the like,

namely, the fact .that these materialsare' free of internal stresses. V o

Other plastics which may be usedaccording to the invention include extruded polypropylene and extruded polyester and polyether products, providedthat they have properties similarto those of polyethylene.

Example 1 A suction box top 4000'millimeters long and 350 wide isto be made and to be-providedwithholes in'a zone having a length of 3000mm. and a width of 280 P mm. The holes are arranged so that relatively wide landsi remain between the .suction holes .of the top. For this purpose, parts of :a non apertured. plate of polyethylene are made: byinjection molding and are then drilled in screwsso that the fastener lies in the: lowermost 10 mm, which is the limit-towhichthe top can bemachined, for

technical reasons. Because thefilands whichremain be:-

tween theholes'have a width. of 15, mm., these parts can be surfaced with any milling,planing or other surfacing machine.

Ex'ampleZ f A suction box top 5000mm. long and500- mm. wide is to be made: in one piece in order to vavoid ,vacuum' defects and uneven portions due to joints and ,to increase the stability of the. top and enable a simple mounting thereof. r

T he, present invention con- It.-is also. of special .im-.

The polishing of the holes 1 5 The activeiwaterv extracting area of this plate is 60% of the zjone fornied with holes. This requires the provision of holes of 12 mm. and the lands remaining between the holes are only 3.5 mm wide. Depending on the fact whether a low or a very low cqefficientof friction required for increasing the wire speed, polyethylene or sintered low-pressure polyethylene having a low molecular weight (about 2 0(:),0 and. a particul arly low coe ilicient of friction will be used. suction 'holes polished to a high finish are also to be used, the use of sintered low-pressure polyethylene having a high molecular weight (about. 1,000,000) is recommended. This material will not take up water and will resist the impacts occurring during mac hining. The chemical stability of thematrial. will a ur that heh h finish w be Preserved during operation even if boiling stock is charged.

Example 3 Suction box strips for use with suction boxes having a strip top are to be made. Th'ese suction box strips may be made, e.g., from non-apertured suction box top plates by cutting them to suitable lehgth. If the strip has an overall thickness of, e.g., 30 him, it may be connected to the suction box by screws disposed in the lowermost 10 mm. I v

The coetficients of friction which have been stated are applicable with re'spect to bronze wire. Wire of other materials, particularly of plastic, may be used, provided that this will not result in a substantial increase in the coeflicients of friction stated above.

Embodimentsof the invention are shown by way of example in the drawing. "FIG. '1 "is a side elevation showin'g the wet end of a paper machine. FIG. 2'is a perspective view showing a siictioh' box top. FIG. 3 is ana mentary topplan view showing a suction box top and FIG. "'4 is a fragmentary plan view of a difierent form of a suction box top.

In the wet end of the paper machine shown in FIG. 1, a machine wire 1 runs around a breast roll 2 and a lower couch roll 3. The lower couch roll 3 is driven by an electric motor 4 and forms the driving member for the wire 1. The breast roll 2 is a reversing roll, which is not driven. The direction of rotation of the lower couch roll 3 is indicated by arrow 5 and the direction of movement of the wire 1 is indicated by arrow 6. The stock consisting of fiber pulp is charged from a hopper 7 onto the wire 1. The wire runs over a forming board 8, which is closed at its top by an apertured top 9. The forming board 8 is formed by a trough, into which a large portion of the liquid is drained out of the stock through the apertured top 9. From the latter, the wire 1 moves over a plurality of wire guide rolls 10, which cause further liquid to drain through the wire. The liquid flows from the wire guide rolls 10 into a trough 11 which constitutes at the same time a frame of the machine.

Behind the wire guide rolls, considered in the direction of movement of the wire, suction boxes 12 are arranged, which are closed at the top by suction box tops 13, over which the wire 1 moves. The suction box tops 13 have the same design as the top 9 and in FIG. 2 it will be seen that length l of the suction box top 13 corresponds to the width of the machine. These suction box tops 13 are in one piece and their longitudinal edge 14 extends transversely to the direction of movement of the wire 1 as shown by the arrow 6. The suction boxes have the form of hollow troughs and are connected by conduits 15 to a vacuum pump 16, by which a vacuum is produced in the suction boxes 12. The suction box tops 13 are formed with holes 17, over which the liquid is sucked out of the stock through the wire 1. Behind the last suction box 12 the wire 1 runs over a deflecting roll 18 to the lower couch roll 3. 19 is the upper couch roll, which is not driven and serves only to press the wire and the web of stock 20 lying on the wire. Behind the couch 6 roll, the web of stock 20 is removed and passed onto the dryer felt, which is not shown.

The returning lower course of the wire is designated at1. This returning course 1' moves overstationary guide rolls 2'1, 22 and vertically adjustable rolls 23 back to the breast roll 2. 24 is a dancer roll. The machine wife 1 is endless and the tension of the wire is adjusted by the vertically adjustable rolls 23' and the dancer roll 24 The lowering of the vertically adjustable rolls 23 will increase thete'nsion of the wire. These vertically adjustable rolls 23 can be adjusted in accordance with the length of the wire. The dancer roll 24 is pivotally movable about a shaft 25 and is urged by gravity onto the wire 1 to effect anautomatie adjustment of the tension of the wire. The tension of the wire 1 must be so high that the lower couch roll 3 i's capable of driving the wire.

FIG. 3 is a topplan viewjshowin'g a portion of the suction box top 13. It serves to define the expression active water extracting area. A rectangle having sides a and b is shown in dotted lihes and is assumed to have an area Y. The cross-sectional areas. of the circular holes in the rectangle 11, 12 is assumedto be X. The active water extracting area equals the quotient X Y This active zone water extracting suction area is at least 40% of the waterextracting 'zone. I

The circular holes 17 may be replaced by elongated holes extending transversely to the direction of movement of the wire.

FI G 4 is a top vplan view showing a suction box top 13 which is formed 'by'spaced apart strips 26 which extend transversely to the direction of movement 6 of the wire 1. Inserts 28 are provided. between the strips 26 at the'edges 27 of the top 13. The spaces 29 between the strips 26 form the suction holes.

What we claim is: y

1. In a machine for treating paper or pulp, a machine wire for receiving the material to be treated, a wire driving roller and means coop'erable with the Wire for extractingwater frointh'e material to be treated, said means having'top's provided with sliding surfaces on which the machine wire slides, said tops being composed substantially of a polyethylene-plastic softer than the material of the wire, the coefiicient of friction between the machine wire and the tops being less than 0.12 so that the speed of the wire is increased, the tops formed only from this plastic being stable in shape and of sufiicient thickness to be self-supporting and have an active water extracting area of at least 40% of the water extracting zone to increase the extraction of water from the stock.

2. The machine as claimed in claim 1, wherein the polyethylene-plastic is sintered low-pressure polyethylene.

3. The machine as claimed in claim 1, wherein the polyethylene-plastic is molded polyethylene.

4. The machine as claimed in claim 1, wherein the polyethylene-plastic is extruded polyethylene.

5. The machine as claimed in claim 1, wherein the polyethylene-plastic is sintered low-pressure polyethylene having a molecular weight of about 1,000,000.

6. The machine as claimed in claim 1, wherein the polyethylene-plastic contains admixtures for reducing friction.

7. The machine as claimed in claim 1, wherein the polyethylene-plastic contains admixtures which are electrically conducting for dissipating electrostatic charges.

8. The machine as claimed in claim 1, wherein the polyethylene-plastic contains admixtures for reducing friction and admixtures which are electrically conducting for dissipating eletrostatic charges.

9. The machine as claimed in claim 1, wherein the polyethylene-plastic contains the admixtures of the group consisting of molybdenum sulfide powder or molybdenum disulfide powder in an amount up to 3 percent by weight for reducing friction.

10. The machine as claimed in claim 1, wherein the polyethylene plastic contains admixtures consisting of graphite powder in an amount up to 3 percent by Weight for dissipating electrostatic charges.

. 11..The machineas claimed in claim 1, whereinthe polyethylene-plastic contains admixtures of the group consisting of molybdenum sulfide powder or molybdenum di-1 sulfide powder and graphite powder and in an amount up to 3 percent by weight'for reducing friction and dissipating electrostatic charges, respectively.

12. The machine as claimed in claim 11, wherein the plastic material contains about /2 percent by weight of molybdenum sulfide powder or molybdenum disulfide powder and about /2 percent by weight of graphite powder.

13. The machine as claimed in claim 1, wherein the polyethylene-plastic contains admixtures for reducing friction with the particle sizes of the admixtures being be-- tween 5 microns and 0.2 micron.

14. The machine as claimed in claim 1, wherein the polyethylene-plastic contains admixtures which are electrically conducting for dissipating electrostatic charges with the particle sizes of the admixtures being between 5 microns and 0.2 micron.

15. The machine as claimed in claim 1, wherein the polyethyleneeplastic contains admixtures for reducing fric-.

tion and admixtures which are electrically conducting for dissipating electrostatic charges with the particle sizes of the admixtures being between 5 microns and 0.2 micron.

16.'The machine as claimed in claim 1, wherein the polyethylene-plastic contains admixtures for reducing fric-,

tion with the particle sizes of the admixtures being be:

tween 2 microns and 0.5 micron.

17. The machine as claimed in claim 1, wherein the: polyethylene-plastic contains admixtures which are electrically conducting for dissipating electrostatic charges with the particles sizes of the admixtures being between 2 microns and 0.5 micron.

18. The machine as claimed in claim 1, wherein the polyethylene-plastic contains admixtures for reducing fric-. tion and admixtures which are electrically conducting for dissipating electrostatic charges with the particle sizes of 7 8? the admixutres being between 2 microns and 0.5 micron. 19. The machine. as claimed in claiml, wherein each top of each means for: extracting water from the stock is in one, piece.

20; The machine as claimed in claim 1, wherein the;

sliding surfaces. of the: tops are polished:

21. The machine as claimed in claim ng-wherein the coefficient of. friction between the -Wire and the sliding surfaces of the tops is less than 0.1.

22. The machine as claimed in claim 1, wherein the tops are provided with polished holes.

23. The machine as claimed :in claim 1, wherein the active water extracting area isat least of thewater extracting zone.

24. The machine as claimed in' claim 1, wherein :the

active water extracting area is about of the water extracting zone.

References Cited by the Examiner OTHER; REFERENCES L Bowden et al.: Friction Behaviour of Plastics Impreg-v nated with Molybdenum vDisulphide, reprinted from Research-vol. 3, No. 8, August 1950.1

Pulp & Paper Manufacture, 1st ed..vol. 3, McGraw-Hill 00.; New York 1953) p. 128.

DDNALL H. SYLVESTER, Primary Examiner.

MORRIS O. WOLIQ Examiner. 

1. IN A MACHINE FOR TREATING PAPER OR PULP, A MACHINE WIRE FOR RECEIVING THE MATERIAL TO BE TREATED, A WIRE DRIVING ROLLER AND MEANS COOPERABLE WITH THE WIRE FOR EXTRACTING WATER FROM THE MATERIAL TO BE TREATED, SAID MEANS HAVING TOPS PROVIDED WITH SLIDING SURFACES ON WHICH THE MACHINE WIRES SLIDES, SAID TOPS BEING COMPOSED SUBSTANTIALLY OF A POLYETHYLENE-PLASTIC SOFTER THAN THE MATERIAL OF THE WIRE, THE COEFFICIENT OF FRICTION BETWEEN THE MACHINE WIRE AND THE TOPS BEING LESS THAN 0.12 SO THAT THE SPEED OF THE WIRE IS INCREASED, THE TOPS FORMED ONLY FROM THIS PLASTIC BEING STABLE IN SHAPE AND OF SUFFICIENT THICKNESS TO BE SELF-SUPPORTING AND HAVE AN ACTIVE WATER EXTRACTING AREA OF AT LEAST 40% OF THE WATER EXTRACTING ZONE TO INCREASE THE EXTRACTION OF WATER FROM THE STOCK. 